This invention concerns a process for preparing pigment compositions that are dispersible in resins, as well as the resulting compositions. The utility of the invention lies in the preparation of pigmented plastics.
Dispersibility, ease of handling, and high pigment levels are prime requirements for a pigment concentrate to be used in the manufacture of pigmented plastic products for coloring purposes and appearance improvement. Prior art shows that such a concentrate can be prepared by (a) mixing the plastic and the pigment in a Banbury or 2-roll mill, followed by pelletizing, (b) feeding a liquid color concentrate and a virgin resin into an extruder, or (c) mixing the resin and pigment with an additive, such as wax, to give a reasonably homogeneous concentrate. Some examples show that the upper concentration limits reached for various pigments in the concentrates are, in wt.%: carbon black--30-70; iron oxide--75-85; phthalocyanine blue--20-50; benzidine yellow--20-50; and TiO.sub.2 --50-80. Such pigmented plastic products are disclosed in U.S. Pat. Nos. 3,449,291; 3,775,357; 3,778,288; and 3,844,810.
But these prior art methods have the disadvantages of additional equipment needed for milling, pelletizing and metering, the need for intermediate letdown, and the fact that most concentrates are prepared for only one kind of plastic, such as polypropylene or polyvinyl chloride. All these disadvantages add to the cost of preparing the pigment concentrate.